1. Field of the Invention
The present invention relates to an image forming apparatus and an image formation system.
2. Description of Related Art
In general, an electrophotographic image forming apparatus (such as a printer, a copy machine, and a fax machine) is configured to irradiate (expose) a charged photoconductor with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor (image carrier) on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet, and then heat and pressure are applied to the sheet at a fixing nip to form an image on the sheet.
In addition, image formation systems have been practically used in which a sheet feeding apparatus that feeds a continuous sheet (hereinafter referred to as “long sheet”) such as continuous roll paper and folded paper, and a winding apparatus that winds up the long sheet on which an image has been formed by the image forming apparatus are respectively connected at preceding and succeeding sides of the above-mentioned image forming apparatus.
In the above-mentioned image forming apparatus, when a sheet is conveyed to an image formation position from a sheet feeding section, the sheet may be displaced in a sheet width direction which is perpendicular to the sheet conveyance direction. Such displacement may be caused by, for example, nonuniformity in longitudinal diameter of a roller that conveys the sheet due to manufacturing error, variation in diameter of the roller due to aging degradation, and displacement of sheets stacked in a sheet feeding section. When such displacement occurs in the sheet width direction, the image may be formed at a position different from the position desired by the user during image formation.
Registration movement is known as a method for solving the above-mentioned problem, that is, as a method for accurately aligning the image and the sheet in consideration of the displacement of the sheet. Japanese Patent Application Laid-Open No. 2007-22680 discloses an exemplary registration movement. Japanese Patent Application Laid-Open No. 2007-22680 discloses a registration roller pair disposed at a position preceding the image formation position, and an optical sensor disposed in the vicinity of a position on the downstream side of the registration roller pair in the sheet conveyance direction. To be more specific, the registration roller pair can be moved with the sheet sandwiched therebetween, and are moved with the sheet sandwiched therebetween in the sheet width direction in accordance with the displacement amount of the sheet obtained by an optical sensor. Consequently, the displacement of the sheet in the sheet width direction is corrected, and thus the image and the sheet are aligned.
However, in the case where an image is formed on a long sheet in the above-mentioned image formation system, when the registration roller pair is moved in the sheet width direction in accordance with the displacement amount of the long sheet obtained by the optical sensor, the long sheet is twisted between a conveyance means located at a position on the downstream side of the registration roller pair in the sheet conveyance direction (for example, a roller pair that forms a fixing nip) and the registration roller pair. When the long sheet is twisted, the long sheet on which a toner image is fixed wrinkles, or the toner image formed on the long sheet is deformed.